BACKGROUND OF THE INVENTION
[0001] The present invention generally relates to the field of gas turbine engines. In particular,
the invention relates to a mid-turbine frame for a jet turbine engine.
[0002] Turbofans are a type of gas turbine engine commonly used in aircraft, such as jets.
The turbofan generally includes a high and a low pressure compressor, a high and a
low pressure turbine, a high pressure rotatable shaft, a low pressure rotatable shaft,
a fan, and a combuster. The high-pressure compressor (HPC) is connected to the high
pressure turbine (HPT) by the high pressure rotatable shaft, together acting as a
high pressure system. Likewise, the low pressure compressor (LPC) is connected to
the low pressure turbine (LPT) by the low pressure rotatable shaft, together acting
as a low pressure system. The low pressure rotatable shaft is housed within the high
pressure shaft and is connected to the fan such that the HPC, HPT, LPC, LPT, and high
and low pressure shafts are coaxially aligned.
[0003] Outside air is drawn into the jet turbine engine by the fan and the HPC, which increases
the pressure of the air drawn into the system. The high-pressure air then enters the
combuster, which burns fuel and emits the exhaust gases. The HPT directly drives the
HPC using the fuel by rotating the high pressure shaft. The LPT uses the exhaust generated
in the combuster to turn the low pressure shaft, which powers the fan to continually
bring air into the system. The air brought in by the fan bypasses the HPT and LPT
and acts to increase the engine's thrust, driving the jet forward.
[0004] In order to support the high and low pressure systems, bearings are located within
the jet turbine engine to help distribute the load created by the high and low pressure
systems. The bearings are connected to a mid-turbine frame located between the HPT
and the LPT by bearing support structures, for example, bearing cones. The mid-turbine
frame acts to distribute the load on the bearing support structures by transferring
the load from the bearing support structures to the engine casing. Decreasing the
weight of the mid-turbine frame can significantly increase the efficiency of the jet
turbine engine and the jet itself.
BRIEF SUMMARY OF THE INVENTION
[0005] In a first aspect of the invention, a mid-turbine frame connected to at least one
mount of a gas turbine engine transfers a first load from a first bearing and a second
load from a second bearing to the mount. The mid-turbine frame includes a single point
load structure and a plurality of struts. The single point load structure combines
the first load and the second load into a combined load. The plurality of struts is
connected to the single point load structure and transfers the combined load from
the single point load structure to the mount.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006]
FIG. 1 is a partial sectional view of a gas turbine engine having a mid-turbine frame.
FIG. 2 is a perspective view of the mid-turbine frame.
FIG. 3A is a cross-sectional view of a first embodiment of the med-turbine frame.
FIG. 3B is a schematic diagram of the first embodiment of the mid-turbine frame.
FIG. 4 is a free body diagram of the first embodiment of the mid-turbine frame.
FIG. 5A is a cross-sectional view of a second embodiment of the mid-turbine frame.
FIG. 5B is a schematic diagram of the second embodiment of the mid-turbine frame.
DETAILED DESCRIPTION
[0007] FIG. 1 shows a partial sectional view of an intermediate portion of gas turbine engine
10 about a gas turbine engine axis centerline. Gas turbine engine 10 generally includes
mid-turbine frame 12, engine casing 14, mounts 16, first bearing 18, and second bearing
20. Mid-turbine frame 12 of gas turbine engine 10 has a lightweight design that transfers
the loads from first and second bearings 18 and 20 to a single point load. The design
of mid-turbine frame 12 is also capable of withstanding a large amount of load without
deflecting, increasing its structural efficiency.
[0008] Mid-turbine frame 12 is housed within engine casing 14 of gas turbine engine 10.
Mid-turbine frame 12 is connected to engine casing 14 and first and second bearings
18 and 20. Engine casing 14 protects mid-turbine frame 12 from its surroundings and
transfers the loads from mid-turbine frame 12 to mounts 16. Mid-turbine frame 12 is
designed to combine the loads from first and second bearings 18 and 20 to one point
for a single point load transfer. Due to the design of mid-turbine frame 12, mid-turbine
frame 12 has reduced weight. The weight of mid-turbine frame 12 will depend on the
material used to form mid-turbine frame 12. In one embodiment, mid-turbine frame 12
has a weight of less than approximately 200 pounds (91 kg). For example, mid-turbine
frame 12 formed of a Nickel-based alloy has a weight of approximately 175 pounds (80
kg). Mid-turbine frame 12 is also designed as a functional plenum and does not require
an independent heat transfer plenum. In addition, mid-turbine frame 12 can be integrally
cast as one piece with a cooling air redistribution device as an integral component.
[0009] First and second bearings 18 and 20 are located at forward and aft ends of gas turbine
engine 10, respectively, below mid-turbine frame 12. First and second bearings 18
and 20 support thrust loads, vertical tension, side gyroscopic loads, as well as vibratory
loads from high and low pressure rotors located in gas turbine engine 10. All of the
loads supported by first and second bearings 18 and 20 are transferred to engine casing
14 and mounts 16 through mid-turbine frame 12. Second bearing 20 is typically designed
to support a greater load than first bearing 18, so mid-turbine frame 12 is designed
for stiffness and structural feasibility assuming that second bearing 20 is the extreme
situation.
[0010] FIG. 2 shows an enlarged, perspective view of mid-turbine frame 12 within a cross-section
of engine casing 14. Mid-turbine frame 12 generally includes torque box 22 and struts
24. First and second bearings 18 and 20 (shown in FIGS 1) are connected to mid-turbine
frame 12 by first bearing cone 26 and second bearing cone 28 (shown in FIG. 1), respectively.
First and second bearings cones 26 and 28 are continuously rotating with high and
low pressure rotors and transfer the loads from first and second bearings 18 and 20
to mid-turbine frame 12.
[0011] Torque box 22 has a shell structure and is positioned between first and second bearing
cones 26 and 28 and struts 24. Torque box 22 takes the loads, or torque, from first
and second bearing cones 26 and 28 and combines them prior to transferring the loads
to struts 24, which extend from along the circumference of torque box 22.
[0012] Struts 24 of mid-turbine frame 12 transfer the loads from first and second bearing
cones 26 and 28 entering through torque box 22 to engine casing 14. Each of struts
24 has a first end 30 connected to torque box 22 and a second end 32 connected to
engine casing 14. The loads travel from torque box 22 through struts 24 to engine
casing 14. In one embodiment, struts 24 have an elliptical shape and are sized to
take a load and transfer it in a vertical direction toward engine casing 14. In one
embodiment, nine struts are positioned approximately forty degrees apart from one
another along the circumference of torque box 22. In another embodiment, twelve total
struts are positioned approximately thirty degrees apart from one another along the
circumference of torque box 22.
[0013] FIGS. 3A and 3B show a cross-sectional view and a schematic diagram of a first embodiment
of torque box 22a, respectively, and will be discussed in conjunction with one another.
Torque box 22a is U-shaped and generally includes U-stem 34a and U-branch 36a. U-stem
34a of mid-turbine frame 12 has a first portion 38, a second portion 40, and a U-shaped
center portion 42. U-stem 34a is positioned below torque box 22 and connects first
and second bearing cones 26 and 28 to each other as well as to torque box 22a. First
portion 38 of U-stem 34a extends from center portion 42 towards first bearing 18 and
also functions as first bearing cone 26. Second portion 40 of U-stem 34a extends from
center portion 42 towards second bearing 20 and also functions as second bearing cone
28. First and second bearing cones 26 and 28 are thus part of U-stem 34a and merge
together at center portion 42. The loads of first and second bearing cones 26 and
28 are introduced into torque box 22a at center portion 42 U-stem 34a. Due to the
shell shape of U-stem 34a, mid-turbine frame 12 can handle large loads at a time without
deflecting. U-stem 34a also acts as a protective heat shield and provides thermal
protection to torque box 22a.
[0014] U-branch 36a has a first end 44 and a second end 46. First end 44 of U-branch is
connected to torque box 22a and second end 46 of U-branch 36a is connected to U-stem
34a at center portion 42 of U-stem 34a. By connecting U-branch 36a to center portion
42 of U-stem 34a, U-branch 36a can function as a bearing arm load transfer member.
[0015] FIG. 4 is a free body diagram of torque box 22a connected to first and second bearings
18 and 20. The loads, or reaction forces, from first and second bearings 18 and 20
come through first and second bearing cones 26 and 28, F
bearing1 and F
bearing2, respectively. Reaction forces F
bearing1 and F
bearing2 come in at an angle and intersect at U-stem 34a. The reaction forces are then broken
up into simple vectors with horizontal components H
bearing1 and H
bearing2 and vertical components V
bearing1 and V
bearing2. The horizontal components H
bearing1 and H
bearing2 come in at opposite directions and cancel each other out a center portion 42 of U-stem
34a. Because the horizontal components H
bearing1 and H
bearing2 cancel each other out, only the vertical components V
bearing1+bearing2 are transferred through U-stem 34a and U-branch 36a to torque box 22a. The total
load is thus reduced due to the absorptive components being cancelled at center portion
42 of U-stem 34a.
[0016] FIGS. 5A and 5B show a cross-sectional view and a schematic diagram of a second embodiment
of torque box 22b, respectively, and will be discussed in conjunction with one another.
Torque box 22b is X-shaped and generally includes X-stem 34b and X-branch 36b. Similar
to torque box 22a, first and second bearings 18 and 20 are connected to X-shaped mid-turbine
frame 22b by first and second bearing cones 26 and 28, respectively. The loads from
first and second bearings 18 and 20 travel through first and second bearing cones
26 and 28 respectively, and are transferred to torque box 22b. Torque box 22b then
transfers the load to engine casing 14 and mounts 16.
[0017] X-stem 34b of torque box 22b has a first portion 48, a second portion 50, and an
X-shaped center portion 52. X-stem 34b is positioned below torque box 22b and connects
first and second bearing cones 26 and 28 to each other as well as to torque box 22b.
First portion 48 of X-stem 34b extends from center portion 52 towards first bearing
18 and also functions as first bearing cone 26. Second portion 50 of U-stem 34b extends
from center portion 52 towards second bearing 20 and also functions as second bearing
cone 28. First and second bearing cones 26 and 28 are thus part of X-stem 34b and
merge together at center portion 52. X-stem 34b acts as a protective heat shield and
provides thermal protection to torque box 22b. The loads of first and second bearing
cones 26 and 28 are also introduced into torque box 22b at X-stem 34b.
[0018] X-branch 36b has a first end 54 and a second end 56. First end 54 of X-branch 36b
is connected to torque box 22b and second end 56 of X-branch 36b is connected to X-stem
34b at center portion 52 of X-stem 34b. By connecting X-branch 36b to center portion
52 of X-stem 34b, X-branch 36b can function as a bearing arm load transfer member.
[0019] In operation, X-stem 34b of torque box 22b functions similarly to U-stem 34a of torque
box 22a except that due to the X-shape of center portion 52, there is a scissor action
that causes an additional load and local state of stress at center portion 52. Thus,
while torque box 22b also has increased structural efficiency, the amount of load
that torque box 22b can support before deflecting will be less than the amount of
load that torque box 22a can support.
[0020] The torque box designs of the mid-turbine frame offer a lightweight structure with
increased structural efficiency. The torque box has a single point transfer structure
that delivers the loads from a first second bearing in the gas turbine engine. The
single point transfer structure thus functions partly as a first and a second bearing
cone. The loads from the first and second bearings combine at the single point transfer
structure to a single load transfer point. Because the loads from the first and second
bearings enter the single point transfer structure at an angle, the horizontal components
of the loads cancel each other out. The only remaining force is in the vertical direction.
The loads are combined and transferred to the torque box, which subsequently transfers
the loads to a plurality of struts attached to the torque box. The struts are attached
to an engine casing surrounding the mid-turbine frame, and delivers the load from
the torque box to the engine casing. In one embodiment, the single point transfer
structure has a U-shape. In another embodiment, the single point transfer structure
has an X-shape.
[0021] Although the present invention has been described with reference to preferred embodiments,
workers skilled in the art will recognize that changes may be made in form and detail
without departing from the scope of the invention.
1. A mid-turbine frame (12) connected to at least one mount (16) of a gas turbine engine
(10) for transferring a first load from a first bearing (18) and a second load from
a second bearing (20) to the mount (16), the mid-turbine frame (12) comprising:
a single point load structure for combining the first load and the second load into
a combined load; and
a plurality of struts (24) connected to the single point load structure for transferring
the combined load from the single point load structure to the mount.
2. The mid-turbine frame of claim 1, wherein the single point load structure is U-shaped.
3. The mid-turbine frame of claim 1, wherein the single point load structure is X-shaped.
4. The mid-turbine frame of claim 1, 2 or 3 wherein the first load is transferred to
the mid-turbine frame (12) through a first bearing cone (26) and the second load is
transferred to the mid-turbine frame (12) through a second bearing cone (28).
5. The mid-turbine frame of claim 1, 2 or 3 wherein the single point load structure comprises:
a stem (34a; 34b) for combining the first and second loads into the combined load;
a branch (36a; 36b) connected to the stem (34a; 34b) for absorbing a portion of the
combined load from the stem (34a; 34b); and
a torque box (22a; 22b) having a first end and a second end, wherein the torque box
(22a; 22b) is connected to the stem (34a; 34b) and the branch (36a; 36b) at the first
end and connected to the plurality of struts (24) at the second end.
6. The mid-turbine frame of claim 5, wherein the torque box (22a; 22b) transfers the
combined load from the stem (34a; 34b) and the branch (36a; 36b) to the plurality
of struts (24).
7. The mid-turbine frame of claim 5 or 6, wherein first and second bearing cones (26,
28) are integrated with the stem (34a; 34b).
8. The mid-turbine frame of any of claims 5 to 7, wherein the stem (34a; 34b) provides
thermal protection to the torque box (22a; 22b).
9. The mid-turbine frame of any of claims 5 to 8, wherein the branch (36a; 36b) functions
as a bearing arm load transfer member.
10. The mid-turbine frame of any of claims 5 to 9, wherein the mid-turbine frame (12)
has a weight of less than approximately 200 pounds (91 kg).
11. A single point load structure for transferring a first load from a first bearing cone
(26) and a second load from a second bearing cone (28) of a gas turbine engine (10)
to a plurality of struts (24), the single point load structure comprising:
a stem (34a; 34b) for combining the first and second loads from the first and second
bearing cones (26, 28);
a branch (36a; 36b) connected to the stem (34a; 34b) for absorbing a portion of the
load from the first and second bearing cones (26, 28); and
a torque box (22a, 22b) connected to the plurality of struts (24) for absorbing the
first and second loads from the stem (34a; 34b) and the branch (36a; 36b).
12. The single point load structure of claim 11, wherein the single point load structure
is U-shaped.
13. The single point load structure of claim 11, wherein the single point load structure
is X-shaped.
14. The single point load structure of claim 11, 12 or 13 wherein the first and second
bearing cones (26, 28) are integrated with the stem (34a; 34b).
15. The single point load structure of any of claims 11 to 14, wherein the torque box
(22a; 22b) is a ring structure.
16. A lightweight mid-turbine frame (12) for combining and transferring a first load and
a second load from a first bearing (18) and a second bearing (20), respectively, to
an engine casing (14) housing the mid-turbine frame, the mid-turbine frame comprising:
a stem (34a; 34b) for combining the first and second loads;
a branch (36a; 36b) connected to the stem (34a; 34b) for acting as a bearing arm load
transfer member;
a torque box (22a; 22b) connected to the stem (34a; 34b) and the branch (36a; 36b)
for absorbing the first and second loads from the stem and the branch; and
a plurality of struts (24) connected to the torque box (22a; 22b) for transferring
the load from the torque box to the engine casing (14).
17. The mid-turbine frame of claim 16, wherein the mid-turbine frame weighs less than
approximately 200 pounds (91 kg).
18. The mid-turbine frame of claim 16 or 17, wherein the stem (34a) is U-shaped.
19. The mid-turbine frame of claim 16 or 17, wherein the stem (34b) is X-shaped.
20. The mid-turbine frame of any of claims 16 to 19, wherein the first load is transferred
to the stem through a first bearing cone (26) and the second load is transferred to
the stem through a second bearing cone (28).